The present invention relates to a household appliance for steam generation, comprising a boiler-in turn comprising a heating source for water vaporisation-steam delivery means, and means for adjusting the pressure value of the steam in the boiler, suitable for switching the heating source on/off so as to maintain the steam pressure at a desired value.
The present invention also relates to a method for adjusting the pressure value of the steam in a boiler of a household appliance for steam generation.
Household appliances for steam generation are known.
Typically, such household appliances comprise a heating source for vaporising the boiler water, and means for maintaining a desired pressure value and a desired water level in the boiler.
Document DE 37 20 583 describes an appliance for steam generation comprising a water vaporisation boiler, a pump for feeding water to the boiler, a heating source wound as a spiral around the boiler, two temperature sensors, also wound as a spiral around the boiler, a manometer and a pressure regulator. One of the two sensors is used to detect the heating source temperature and draw water into the boiler when the detected temperature exceeds a first threshold temperature. The second sensor is used to detect the heating source temperature and turn it off when the detected temperature exceeds a second threshold temperature that is higher than the first threshold temperature. The manometer and the pressure regulator are, on the other hand, used for maintaining a desired value of steam pressure in the boiler.
Patent application PCT/ITOO/00112 filed by the Applicant, describes an apparatus for steam generation comprising a water vaporisation boiler, a pump for feeding water to the boiler, a heating source having an elevated portion, a temperature sensor in contact with such elevated portion, and a manometer with associated respective control means. The sensor is used to detect the heating source temperature and draw water into the boiler when the detected temperature exceeds a threshold temperature. In turn, the manometer is used to detect the steam pressure in the boiler, and the control means is used to switch the heating source on/off in function of the pressure value detected by the manometer, so as to maintain a desired steam pressure value in the boiler.
However, the use of the manometer for adjusting the water pressure value in the boiler of the appliances described by the above documents has the disadvantage of implying high costs. Moreover, the manometer exhibits the disadvantage of being relatively cumbersome.
The Applicant has thus faced the technical problem of realising a household appliance for steam generation at reduced costs and cumber.
Thus, in a first aspect thereof, the present invention relates to a household appliance for steam generation, comprising
a boiler comprising, in turn, a heating source for water vaporisation, intended to be at least partly immersed in water,
control means comprising, in turn, means for adjusting the pressure value of the steam in the boiler, said means being operatively associated with the heating source to switch it on/off so as to maintain the steam pressure at a desired value,
steam delivering means,
characterised in that the means for adjusting the pressure value in the boiler is operatively associated with the steam delivery means so as to switch the heating source on/off in function of the open/closed status of the steam delivery means.
The pressure adjusting means of the appliance of the invention regulate the pressure value in the boiler through a simple control of the status (open/closed) of the steam delivery means.
Such function can be performed by simple circuit diagrams which, with respect to the use of a manometer, allow the costs and cumber of the appliance to be reduced.
In the present description and claims, the expression xe2x80x9cstandby conditionxe2x80x9d is used to indicate the situation in which the heating source is immersed in water, the steam pressure in the boiler substantially has the desired value, the boiler is ready to deliver steam and the steam delivery means is closed. In turn, the expression xe2x80x9csteam delivery conditionxe2x80x9d is used to indicate the situation in which the boiler delivers steam, for example, to a user equipment, and the steam delivery means is open or in its opening or closing transient.
Typically, the boiler also comprises a temperature sensor suitable for detecting the heating source temperature.
Preferably, the sensor is in contact with the heating source.
Advantageously, the means for adjusting the pressure value in the boiler is operatively connected to the temperature sensor so as to switch the heating source on/off in function of the temperature value detected by the sensor (12) when the steam delivery means status is closed.
To this purpose, the Applicant notes that when the boiler is in standby condition, the water present into the boiler is in saturation conditions, so that pressure and temperature are connected to one another by a bi-univocal correspondence. Moreover, the temperature detected by the temperature sensor is substantially equivalent to the water temperature. It is thus possible to maintain the desired pressure value in function of the temperature value detected by the sensor.
On the other hand, during the initial heating of the appliance, when the temperature of the water present in the boiler is less than that detected by the temperature sensor, the sensor detects a higher temperature than the actual water temperature. As a consequence, the heating source is switched on/off a certain number of times before reaching the standby desired pressure value. However, this is not a problem since if a user requires steam delivery when the pressure in the boiler has not reached the desired value yet, the means for adjusting the pressure value would keep the heating source on during the opening time of the steam delivery means (see below), thus bringing the pressure to the desired value.
Advantageously, the means for adjusting the pressure value in the boiler is suitable for switching the heating source off when the sensor detects a higher temperature than a first temperature threshold S1 and switching the heating source on when the sensor detects a lower temperature than said first temperature threshold S1.
Preferably, the value of the first threshold S1 corresponds to the value detected by the temperature sensor in standby condition when the steam in the boiler reaches the desired pressure value (for example, 2 bar).
Advantageously, when the status of the steam delivery means switches from closed to open, the means for adjusting the pressure value in the boiler is suitable for switching the heating source on.
This allows the pressure loss in the boiler caused by steam delivery to be remedied immediately.
In fact, the Applicant notes that when the steam delivery means open, the boiler undergoes an immediate pressure loss. Such pressure loss causes a corresponding cooling of the water and of the heating source, and thus, a decrease in the temperature detected by the temperature sensor, with respect to the value of the first threshold S1. However, the temperature detected by the probe decreases at a much slower rate than that at which the pressure decreases. Thus, without the switching of the heating source on upon the opening of the steam delivery means, the heating source would be switched on behind time with respect to the pressure loss, thus delaying the restoration of the desired pressure value.
Preferably, at the switching of the steam delivery means status from closed to open, the heating source is switched on with a predetermined delay with respect to the opening of the steam delivery means. This allows preventing useless switching on of the heating source in case of steam delivery lasting a non significant time.
Preferably, when the status of the steam delivery means is open, the means for adjusting the pressure value in the boiler is suitable for keeping the heating source on.
This allows remedying the pressure loss in the boiler caused by the steam delivery.
To this purpose, the Applicant notes that in steam delivery conditions, pressure and temperature are not connected to each other by a bi-univocal correspondence anymore; thus, it is not advantageous anymore to adjust the pressure value in the boiler in function of the temperature value detected by the sensor.
Advantageously, when the status of the steam delivery means switches from open to closed, the means for adjusting the pressure value in the boiler is suitable for keeping the heating source on for a predetermined time.
At the closure of the steam delivery means, this allows quickly restoring the pressure to the desired value in standby conditions.
In fact, the Applicant notes that during the steam delivery step in which the heating source is kept on by the pressure adjusting means, the water temperature present in the boiler is less than that detected by the temperature sensor. Thus, when the steam delivery step ends, the sensor detects a higher temperature than that effective of water, As a consequence, if it were not kept on for a predetermined period of time after closing the steam delivery means, the heating source would be switched on/off a certain number of times before the boiler returned to the standby saturation condition (in which the water temperature is almost equal to that detected by the sensor) with a consequent delay in restoring the desired pressure value.
Advantageously, said predetermined period of time is selected in function of the period of time in which the steam delivery means has been open.
Preferably, said predetermined period of time is selected in function of the boiler size, of the quantity of water contained therein, and of the heating source power.
For example, said period of time is about 3 times the opening time of the steam delivery means, and it has a maximum value of about 10s.
Advantageously, in steam delivery conditions, the control means of the appliance of the invention is suitable to switch the heating source off when the temperature detected by the temperature sensor is more than a second temperature threshold S2.
This allows the control means to perform a heating source protection function. In fact, when the temperature value of the heating source increases above the value of the second threshold S2, for example due to a failure of the water delivery means described below, they have the function of switching the heating source off.
The second threshold S2 is advantageously higher than the above first threshold S1. For example, S2 is equal to about 165-170xc2x0 C.
Advantageously, in steam delivery conditions, the control means of the appliance of the invention is also suitable to make the heating source be switched on again when the temperature detected by said temperature sensor is once again less than said threshold S2.
In a variant, said control means is suitable to switch the heating source off/on when the temperature detected by the sensor is more/less than the second temperature threshold S2, also when the status of the steam delivery means is closed. This allows performing the heating source protection function also when the steam delivery means status is closed. This may be useful, for example when, due to a failure, the means for adjusting the pressure value does not compare the temperature detected by the sensor with the first threshold S1 anymore.
Typically, the appliance also comprises an atmospheric-pressure water tank.
Advantageously, the appliance also comprises means for feeding water from the tank to the boiler.
Typically, the control means of the appliance of the invention also comprises means for adjusting the water level in the boiler.
Preferably, said means for adjusting the water level in the boiler is operatively associated with the temperature sensor and to the water feeding means, so that the latter provide water to the boiler when the temperature sensor detects a higher temperature than a third temperature threshold S3.
Moreover, the water feeding means advantageously interrupts the water inflow to the boiler when the temperature sensor detects a lower temperature than the third temperature threshold S3.
Typically, the means for water feeding from the tank to the boiler comprises an electrical micro-pump. Advantageously, said electrical micro-pump is of the vibrating type.
Preferably, as the appliance of the invention is switched on, the water level adjusting means is suitable for driving said water feeding means so that they supply a quantity of water to the boiler. More preferably, said water level adjusting means is suitable for driving said feeding means when the appliance of the invention has been switched off for a long period of time. This aspect of the invention is advantageous since during the switching on step, when the water volume in the boiler is less than in standby conditions, it prevents the heating source from emerging from water, thus overheating. In fact, upon switching on, passing from an ambient temperature to a standby temperature (for example of 140-145xc2x0 C.), the water in the boiler undergoes a volume expansion (generally, of at least 6%).
Moreover, the above feature allows the electrical micro-pump to be triggered before steam is generated in the boiler. This is advantageous for vibrating pumps since such pumps can exhibit triggering problems when the boiler is already pressurised.
Advantageously, the water tank comprises a sensor suitable for detecting the water level contained therein.
Preferably, when the water level detected by such sensor is less than a predetermined threshold value, the control means switches on a user warning light and deactivates the water feeding means and the heating source. This advantageously allows the need to fill the water tank to be signalled to the user and to prevent the water feeding means and the heating source from continuing to operate when the water in the tank is finishing.
Advantageously, when the water level detected by said sensor is less than said predetermined threshold value, said control means also provides for the closure of said steam delivery means. This allows the boiler to be kept ready to deliver steam again, preventing the userxe2x80x94that has not noticed the signalling warning light of the tank water levelxe2x80x94from continuing to request steam delivery, thus emptying the boiler. In fact, emptying the boiler would cause a delay in restoring the appliance operating conditions, after filling the water tank, due to the time required by the boiler to be filled with water again and to the time required by water to be vaporised again at the desired conditions.
In a preferred embodiment, the heating source has an elevated portion.
Advantageously, the temperature sensor is suitable for detecting the temperature of the elevated portion of the heating source.
This embodiment is advantageous since when the water level in the boiler decreases, only the elevated portion of the heating source emerges from water, thus allowing the remaining part of the heating source to substantially operate immersed in water, preventing frequent increases of temperature of the entire heating source, which may impair its good operation and life.
Preferably, the elevated portion of the heating source extends along a predetermined direction.
Typically, the temperature sensor is contained in a protective envelope.
Advantageously, the temperature sensor protective envelope is in contact with the elevated portion of the heating source along a contact portion extending along said predetermined direction, so as to make the contact portion relatively wide.
This allows the sensor to be located with respect to the elevated portion in a more reliable way. In fact, for a correct operation of the appliance, the exact portion of the protective envelope in which the sensor is, must be welded on the elevated portion of the heating source. A minimum error in positioning the protective envelope on the elevated portion may cause a wrong positioning of the sensor with respect to the heating source.
Moreover, the relatively wide contact portion between the protective envelope and the elevated portion advantageously allows, when assembling the appliance of the invention, the positioning of the sensor inside the protective envelope and of the protective envelope with respect to the elevated portion of the heating source to be facilitated. In fact, a relatively wide contact portion allows the tolerances of such positionings to be increased.
Advantageously, the contact portion between said protective envelope and said elevated portion has an extension at least equal to 5 mm. Preferably, said extension is comprised between 5 and 30 mm. This allows to have a good margin for arranging the sensor protective envelope with respect to the elevated portion. Advantageously, said elevated portion extends in a substantially rectilinear manner.
According to an alternative, said elevated portion substantially extends according to a circumference arc.
Typically, said heating source is substantially U-shaped, comprising two substantially rectilinear and parallel opposed portions and a curvilinear portion connecting the two rectilinear portions.
In this case, said elevated portion is preferably located at one of the two rectilinear portions of said U-shape.
According: to an alternative, said elevated portion is located at the curvilinear portion of said U-shape.
According to an alternative, said heating source can, for example, be shaped as a U folded on itself, or as a spiral.
The size of the heating source is advantageously selected in function of the desired power and of the size of the boiler intended to contain it.
Preferably, said protective envelope is welded along said elevated portion. More preferably, said protective envelope is welded along an upper part of said elevated portion. In this way, the elevated portion of the heating source is prevented from emerging from water before the temperature sensor and, thus, from undergoing an increase of temperature without the sensor detecting it correctly.
Preferably, said welding is performed through brazing. This advantageously allows avoiding, in the course of time, limestone deposits along the contact portion between the thermal source and the protective envelope, and thus a decrease in the sensor sensitivity.
Advantageously, said protective envelope has an elongated body. Typically, said envelope is a stainless steel tube.
Typically, said heating source is an electrical resistor. Advantageously, the boiler also comprises a fuse. Preferably, said fuse is welded on said elevated portion, in opposed position with respect to said temperature sensor. The fuse is suitable to bum and thus to deactivate the heating source when it reaches a predetermined dangerous temperature (for example equal to about 190xc2x0 C.). This allows the appliance of the invention to be protected from excessive temperature increases of the heating sourcexe2x80x94due, for example, to a failure of the temperature sensor or of the water feeding meansxe2x80x94which may be dangerous.
In a second aspect thereof, the present invention relates to a method for adjusting the steam pressure in a boiler, comprising a heating source intended to be at least partly immersed in water for water vaporisation, said boiler being associated with steam delivery means, said method comprising the steps of
a) powering the heating source at the appliance switching on;
b) switching the heating source on/off so as to maintain the steam pressure in the boiler at a desired value,
characterised in that it also comprises the step c) of checking the open/closed status of the steam delivery means, and in that step b) is carried out in function of the open/closed status detected in step c).
According to the method of the invention, the steam pressure in the boiler is maintained at a desired value by operating on the switching on/off of the heating source in function of the open/closed status of the steam delivery means.
This allows the pressure of a boiler to be adjusted without a direct detection of the pressure value, thus avoiding the expensive and relatively bulky use of a manometer.
Preferably, when the status detected in step c) is closed, step b) is carried out according to a step b2) of detection of the heating source temperature and of switching on/off of the heating source in function of the detected temperature.
Typically, step b2) is carried out switching the heating source off when the detected temperature value is more than a first threshold temperature S1.
Typically, step b2) is further carried out switching the heating source on when the detected temperature value Is less than the first threshold temperature S1.
Advantageously, when in step c) a passage from closed to open of the steam delivery means is detected, step b) is carried out according to a step b3) of switching the heating source on.
Preferably, in step b3) the heating source is switched on with a predetermined delay with respect to the passage of the steam delivery means from closed to open.
Preferably, when the status detected in step c) is open, step b) is carried out through a step b4) according to which the heating source is kept on.
Advantageously, when in step c) a passage from open to closed of the steam delivery means is detected, step b) is carried out through to a step b5) according to which the heating source is kept on for a predetermined period of time.
Advantageously, when the status detected in step c) is open or when in step c) a passage from open to closed or from closed to open of the steam delivery means is detected, the method of the invention also comprises the step d) of detecting the temperature of the heating source and switching the heating source off when the detected temperature value is more than a second temperature threshold S2. According to an embodiment, step d) is carried out also when the steam delivery means status detected in step c) is closed.